Everything type matter is branded in the physical world with properties that define what it is and how it behaves when in the presence of other substances. These properties give the substance, whatever it may be, its own distinctive features that can be used to identify it. These properties can be determined by measuring and observing the material under different conditions. But any substance will have not just one set of properties, but two sets of different properties. These two sets will be physical properties and chemical properties.
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A physical property is a feature of a substance that can be observed without changing the identity of the substance. Many of these properties are properties that we can see with our eyes or feel with our hands, such as texture, shape, color, size, or smoothness. Even things such as conductivity, malleability, and ductility are physical properties. There are also two different kinds of physical properties. Intensive physical properties are features that will be the same no matter how much of the substance is present. On the other hand, extensive physical properties are properties that do depend on the amount of the substance present, such as mass, volume, length, and height. These are all physical properties because they can all be observed without making the substance into a different substance.
As soon as the substance is turned into a different substance, it is considered a chemical property. Chemical properties describe the ability of a substance to change its identity. Anything that can be done to a substance that will change its identity is considered a chemical property, such as its flammability (in case of a fire) or its reactivity (how it reacts to other chemicals). If a substance changed into a different substance through a chemical reaction, then it has a chemical property related to that change. The change it went through is a chemical change.
Chemical changes can also be called chemical reactions. In a chemical change, the identity of a substance will be changed, and it will have different properties. These changes can be shown in a chemical equation, like this:
HCl + NaOH ƒ NaCl + H2O
This equation shows than when HCl, a strong acid, reacts with NaOH, a strong base, the chemical reaction results in sodium chloride (NaCl) and water (H2O). Physical changes can also occur. The difference is that instead of the substance changing its identity, it changes form. After a physical change, the properties of the substance will remain the same. There are three main types of physical changes. The first is mechanical physical change, such as tearing, crushing, or breaking a substance. Second, a solution could be made, like when salt is dissolved in water. No ‘new’ substances are formed even though the salt is dissolved. The salt could still be filtered out. Thirdly, changes in the state of matter are also a physical change. Water that changes from a solid to a liquid to a gas is all physical changes. The equation to show this looks like this:
H2O(s) ƒ H2O(l) ƒ H2O(g)
The letters in the subscript convey what state of matter the H2O is in. The ‘s’ stands for solid, the ‘l’ for liquid, and the ‘g’ for gas. The reason it is a physical change is because the chemical make-up of the substance is still the same throughout. If the chemical make-up of the substance changes, then it is a chemical change.
Problem: To carry out several chemical & physical changes to judge whether they are chemical or physical.
Hypothesis: It is expected that the chemical changes will cause much more noticeable observations
Materials:
-Match
Eyedropper
-Candle (held stationary by clay)
-10 drops of 0.1 M AgNO3 (silver nitrate)
-Wooden splint
-One piece (about 3cm) of Magnesium (Mg)
-2 Watch Glasses
-10 drops of 6 M HCl (concentrated
hydrochloric acid)
-Small spatula of NaCl
-Tongs
-10 mL of water (divided up into 2, 5mL
divisions)
-Bunsen Burner
-2 Test tubes
-Mortar and Pestle
-Test tube cork
-CuSO45H2O (Copper II sulfate pentahydrate)
-A few filings of Fe (iron)
Diagrams:
*On attached pages*
Procedure:
Light a match and use it to light a candle held stationary by a piece of clay. Observe the flame, the wick, and the wax for several minutes. Record observations.
Obtain a wooden splint and break it in half. Place the end of one half of the wooden splint into the candle flame. Extinguish the flames of both the candle and the splint. Place the splint into a watch glass and observe. Record observations. Dispose of the wood in the designated waste container.
Place a small spatula of NaCl (sodium chloride) into a small test tube. Add 5 mL of water. Cover the test tube with a test tube cork and shake the contents of the tube. Record observations. Save the product for Step 4.
Use an eyedropper to add 10 drops of a 0.1 M AgNO3 (silver nitrate: do not get this on you!) solution to the salt-water solution which was made in Step 3. Cover the tube with a cork and fully invert several times to mix properly. Record observations. Dispose in the designated waste container.
Obtain one piece of Mg (magnesium) ribbon about 3 cm long. Tear it into 2 pieces. Place one piece into a test tube. Use a pipet to add 10 drops of 6 M HCl (concentrated hydrochloric acid). Record observations. Dispose in the designated waste container.
Handle the other piece of Mg with tongs. Place the Mg into the hottest part of the burner flame at the front lab table for a few minutes until a noticeable change occurs. Caution: Do not look directly into the light! Place the product on a watch glass. Record observations. Dispose in the designated waste container.
Use a mortar and pestle to grind several crystals of CuSO45H2O (copper II sulfate pentahydrate) into a uniform powder. Record observations. Place a small spatula of the CuSO45H2O powder into a test tube. Add 5 mL of water, cap it with a cork, and invert fully several times to mix. Record observations. Save the product for Step 8.
To the test tube containing the water and CuSO45H2O, add a few Fe (iron) filings. Cap it with a cork and invert fully several times to fully mix. Look very closely into the test tube. A keen observer gets the proper results. Record observations. Dispose in the designated waste container.
Data:
Step
Physical Properties of Starting Materials
Observations of The Change
1
Candle looks waxy, with few drops dried on the side. It is a pale white color. It appears to be slightly burnt. The bottom clay is a bright yellow and has a smooth texture.
Wax on the top melts and forms a liquid. Tip of wick is a bright red color. More drips start to appear on the side of the candle. As the wax drips down, it changes from clear to pale white, while also hardening.
2
Wood is smooth, light brown in color, and very brittle. It is small and rectangular. The watch glass is clear, with cloudy material on bottom of glass.
The wood starts to wilt and shrivels, while turning black, with a red tip. Little bits of ash appear. Smoke rises from the flame, and it smells faintly of ham.
3
Sodium chloride looks clear, crystalline, and very granular. Some of the NaCl sticks to the side of the container.
NaCl dissolves into the water to make a solution. Clear liquid in test tube.
4
AgNO3 looks cloudy on the surface of the water. It is an opaque white color and sticks together.
Seems to form a heterogeneous mixture, with white specks of AgNO3 floating in the water. The water solution became chunky and cloudy.
5
Silver in color, malleable, small, thin, rectangular in shape. It is smooth on the surfaces and kind of sharp on the corners. It is 3cm in length.
Test tube gets hot; piece of magnesium starts to disintegrate. At the end, ash is left at the bottom and what looks like smoke rises from the top. Liquid looks slight yellow.
6
Piece of magnesium looks the same as above.
Magnesium starts to burn and then quickly turns into a bright white light as the flame gets really intense. There is a slight change in heat because the amount of flame increased.
7
Crystals look deep blue. There is no odor present. They look smooth, but clear-cut. They hold their shape.
The water turns blue and the powder is dissolved. The liquid does look see-through.
8
(see part 2 of step 7)
The liquid turns into a dirty brown color. The Fe seems to sink to the bottom of the test tube. It doesn’t look like Fe anymore, though. It looks like copper because of its color.
Questions:
Intensive properties are properties that will not change based on the amount of a substance you have. Some examples from the lab are the waxiness of the candle, the color of the magnesium, or the malleability of the magnesium. An extensive property will change based on the amount of a substance you have. Examples of these properties (from the lab) are the size of the wooden splint, the length of the magnesium strip, or the height of the candle.
a. Lighting a match: Chemical. The physical make-up of the wood and its head is changed.
b. Melting wax: Physical. The wax is still wax, it’s just in a different form.
c. Burning a wick: Chemical. The wick slowly burns down and changes its make-up.
d. Freezing wax: Physical. It is still wax.
e. Breaking wood splint: Physical. It is still wood.
f. Burning wood: Chemical. It is a different material after you burn it.
g. Dissolving sodium chloride: Physical. It is still salt. You could filter the salt back out of the solution.
h. Reacting NaCl and AgNO3: Chemical Change. The two compounds change their molecular make-up.
i. Breaking and sanding Mg: Physical. It is still magnesium; it’s just in a different form.
j. Burning magnesium: Chemical. The magnesium is no longer magnesium and goes through a chemical reaction.
k. Adding acid to Mg: Chemical. In the reaction, the Mg is changed.
l. Crushing copper II sulfate: Physical. It is still copper II sulfate; it’s just been changed to a different form.
m. Dissolving copper II sulfate: Physical. It is still the same material.
n. Adding Fe to copper II sulfate: Chemical. The Fe changed because it bonded with So4.
The change involving a candle is both chemical and physical because the candle wax is melting, which is a physical change to the candle, but the candle wick is also burning, which is a chemical change. The candle wax is remaining as wax; it’s just changing from a solid to a liquid. When it cools down, it forms a solid again. The wick, however, never returns to its previous state after being burned. It is no longer a candle wick.
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Two changes in the experiment that were exothermic were the wooden splint burning and the magnesium reacting with the hydrochloric acid. Wooden splint had a flame on it (when it was burning) that gave off a lot of heat. The magnesium caused the test tube to become extremely hot. A change in the experiment that was endothermic was when we melted the candle wax. The wax had to take in a lot of energy from the flame in order to do a physical change into a liquid.
In chemical changes, the formulas of reactants compare to the formulas of the product because they are different. The substances are changed in a chemical change, so their molecular make-up will also change. For example, in Step 8, we had the reactants CuSO4 and Fe. But the products weren’t the same.
CuSO4 ƒ Cu +FeSO4
The iron bonded with the SO4, leaving copper behind. In a physical change, the formulas will be the same on each side. The only thing that might change is its state of matter.
H2O(s) ƒ H2O(l)
The chemical make-up is still the same, but it did change from a liquid to a gas. The formulas on each side have to stay the same though.
Data Analysis:
Based on the observations collected, 3 of the 8 steps performed were physical changes. Step 1, the burning of the candle, was surprisingly a physical change. What made this clear is that it could be observed that the wax is only melting, not changing to a different substance. Due to background information, it can be concluded that this is a physical change. Step 3 involves dissolving NaCl in water, which is also classified as a physical change. Step 7 is just like step 3 in that a substance was dissolved in water, so this is also a physical change.
Several chemical changes also occurred. Step 2, the burning of the wooden splint, marked a chemical change because the step started out with a piece of wood observed as smooth, light brown in color, and very brittle. After the change, it wilted and shriveled to a black substance with all new properties. Since it has transformed into a new substance, it can be concluded that this is a chemical change. The AgNO3 in step 4 reacts with the NaCl and the H2O to form a new substance in the liquid, which creates small, floating particles. Since a new substance was formed inside the liquid, this is also a chemical change. The magnesium reacting with the acid as well as being burned in the Bunsen burner was both chemical changes because neither of the changes warranted any magnesium afterwards, so it is known that a chemical change occurred. Lastly, the CuSO4-2 reacted with the Fe+2 to create different substances, namely Cu and FeSO4. It can therefore be concluded that this was also a chemical change.
Error:
A few things may have caused errors in this experiment, but because the results were not dependent on extremely precise amounts of any substance, getting the appropriate results was fairly easy. However, if the wrong substance had accidentally been placed in a test tube instead of another substance, the results will be completely different than what they are supposed to be. This could also result in a dangerous situation depending on what substance had been replaced. Another thing that may have hindered the results of the burning of the magnesium is if the flame wasn’t hot enough to burn the magnesium or the piece of magnesium was somehow flawed, where it wouldn’t burn. Another thing that would obstruct the correct results is if any test tube broke while it was in use, for it couldn’t be used to observe the changes occurring anymore. If the candle (from step 1) had so much wax that the wick wasn’t exposed enough to light, then it would have made it difficult to perform the first couple steps of the experiment. Error can come from many different sources, but human error is the most frequent type of error.
Conclusion:
It was attempted to perform a variety of experiments to carry out chemical and physical changes. Then, it was judged what kind of change it was. Success was reached in doing this. Chemical changes were observed, such as the wooden splint burning, the magnesium bubbling, and the SO4-2 bonding to the Fe+2. Physical changes were also observed, such as the candle wax melting, the NaCl dissolving in the water, and ripping the magnesium strip in half. A lot was definitely learned about the difference between chemical and physical changes, and how to distinguish between the two.
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